1. Field
One or more embodiments of the present disclosure relate to a method of driving a motor using an inverter, and more particularly to driving a plurality of permanent magnet synchronous motors (PMSM) using a single inverter.
2. Description of the Related Art
As for driving of a PMSM, an inverter is needed to apply a voltage level required to drive the PMSM. The voltage level of the PMSM may be variable depending on the speed and torque of the PMSM and a rotator flux position. In particular, a voltage phase may be variable according to a rotator flux position.
A vector control method is mainly used for driving the PMSM. In the vector control method, voltage is applied to place vector current at a position that is electrically forward from a rotator magnetic flux position by 90 degree. Therefore, when a plurality of PMSMs are driven, the same number of inverters is needed.
When a single inverter is used to drive a plurality of PMSMs, the plurality of the PMSMs may be connected to the inverter in parallel. Stator coils on each phase of the plurality of PMSMs may be connected to a leg of the inverter corresponding to each phase so that the same voltage is applied to each PMSM of the plurality of PMSMs. The applied voltage level may be determined according to the voltage required by the PMSM having the largest load among the plurality of PMSMs.
In the plurality of PMSMs in parallel using a single inverter, the same voltage level is applied to the plurality of PMSMs. If the plurality of PMSMs have the same parameter and load, the plurality of PMSMs may have the same performance. However, in practice, the plurality of PMSMs may have different parameters and loads due to manufacturing differences, so rotator positions may be variable in the plurality of the PMSMs. Therefore, the plurality of PMSMs each require different voltage levels. Various voltage levels, however, cannot be generated by a single inverter.
In a conventional parallel structure, a plurality of PMSMs may be driven at the same speed, and one or more of the plurality of PMSMs may be stepped out when the difference between the rotor positions is increased due to the difference in speed of the PMSMs from each other. In the conventional parallel structure, in order to confirm the current being applied to the plurality of PMSMs, at least two current sensors may be needed for each PMSM. For example, when N PMSMs may be driven by a single inverter, 2N current sensors may be needed in total.